Explosions of homemade bombs were reported in Bangladesh's capital Tuesday as opposition activists enforcing a daylong general strike rioted and clashed with police.

Police fired tear gas to disperse crowds of people who were smashing vehicles. It was not immediately clear if anyone was injured in the violence described by witnesses and television reports in parts of Dhaka.

A coalition of 18 opposition parties was enforcing the strike to demand that a caretaker government be formed before the next national elections due in 2014. A key coalition partner also wants its leaders facing charges of crimes against humanity to be freed from jail.

Schools and businesses were closed in Dhaka and other major cities and transportation was largely disrupted across Bangladesh, a parliamentary democracy that has a history of fierce political violence.

The United States on Tuesday urged the two main political parties to hold a dialogue to find a solution to the political impasse.

Robert O. Blake, the U.S. assistant secretary of state for South and Central Asian affairs, said in Dhaka that the U.S. would support any resolution coming from the two major parties.

Independent television reported the detention of at least six opposition activists from the Dhaka University area in the capital.

Police said activists torched at least 21 vehicles in Dhaka late Monday after police arrested a senior leader of the main opposition Bangladesh Nationalist Party, led by former Prime Minister Khaleda Zia.

Jamaat-e-Islami, the country's largest Islamic party and the main partner of Zia's party, has been demanding the release of nine of its leaders facing charges of crimes against humanity dating back to the 1971 independence war against Pakistan. Two other leaders from Zia's party face similar charges and are now jailed.

Zia has criticized the trial, calling it a farce.

In 1971, Bangladesh - at the time the eastern wing of Pakistan - became independent after a nine-month war with the help of India, Pakistan's bitter rival.

Jamaat-e-Islami leaders are accused of aiding the Pakistani army in killing and raping during the war. The party says the charges are politically motivated.

Police said Mirza Fakhrul Islam Alamgir, acting secretary general of Zia's party, was arrested Monday on charges of instigating violence and burning a vehicle during a nationwide road blockade on Sunday.

The opposition said it would enforce another general strike Thursday unless Alamgir and others detained during the violence are freed by Wednesday.

Opposition spokesman M.K. Anwar said at least 250 people were detained Tuesday.

Dozens of vehicles were burned and smashed Sunday and at least two people died during the opposition-sponsored blockade.

Last year, the government of Prime Minister Sheikh Hasina scrapped a 15-year-old caretaker government system during elections following a Supreme Court ruling that the constitution allows only popularly elected governments. Opposition parties fear the election will be rigged if the current party remains in power.

The government has blamed the opposition for the recent violence, saying the protests are aimed at protecting the 1971 suspects. The administration has vowed not to go back to the caretaker government system.

Hasina's Awami League party and Zia's Bangladesh Nationalist Party are the main contenders for power.